KNOCKHARDY PUBLISHING AN INTRODUCTION TO CARBOXYLIC ACIDS AND THEIR DERIVATIVES KNOCKHARDY PUBLISHING

KNOCKHARDY PUBLISHING CARBOXYLIC ACIDS INTRODUCTION This Powerpoint show is one of several produced to help students understand selected topics at AS and A2 level Chemistry. It is based on the requirements of the AQA and OCR specifications but is suitable for other examination boards. Individual students may use the material at home for revision purposes or it may be used for classroom teaching if an interactive white board is available. Accompanying notes on this, and the full range of AS and A2 topics, are available from the KNOCKHARDY SCIENCE WEBSITE at... www.argonet.co.uk/users/hoptonj/sci.htm Navigation is achieved by... either clicking on the grey arrows at the foot of each page or using the left and right arrow keys on the keyboard

CARBOXYLIC ACIDS CONTENTS Structure of carboxylic acids Nomenclature Physical properties of carboxylic acids Preparation of carboxylic acids Chemical properties of carboxylic acids Esters Acyl chlorides Revision check list

Before you start it would be helpful to… CARBOXYLIC ACIDS Before you start it would be helpful to… Recall the definition of a covalent bond Recall the difference types of physical bonding Be able to balance simple equations Be able to write out structures for simple organic molecules Understand the IUPAC nomenclature rules for simple organic compounds Recall the chemical properties of alkanes and alkenes

STRUCTURE OF CARBOXYLIC ACIDS • contain the carboxyl functional group COOH • the bonds are in a planar arrangement

STRUCTURE OF CARBOXYLIC ACIDS • contain the carboxyl functional group COOH • the bonds are in a planar arrangement • include a carbonyl (C=O) group and a hydroxyl (O-H) group

STRUCTURE OF CARBOXYLIC ACIDS • contain the carboxyl functional group COOH • the bonds are in a planar arrangement • include a carbonyl (C=O) group and a hydroxyl (O-H) group • are isomeric with esters :- RCOOR’

Carboxylic acids form a homologous series HCOOH CH3COOH C2H5COOH

Carboxylic acids form a homologous series HCOOH CH3COOH C2H5COOH With more carbon atoms, there can be structural isomers C3H7COOH (CH3)2CHCOOH

INFRA-RED SPECTROSCOPY IDENTIFYING CARBOXYLIC ACIDS USING INFRA RED SPECTROSCOPY Differentiation Compound O-H C=O ALCOHOL YES NO CARBOXYLIC ACID YES YES ESTER NO YES ALCOHOL CARBOXYLIC ACID ESTER O-H absorption O-H + C=O absorption C=O absorption

NAMING CARBOXYLIC ACIDS Acids are named according to standard IUPAC rules • select the longest chain of C atoms containing the COOH group; • remove the e and add oic acid after the basic name • number the chain starting from the end nearer the COOH group • as in alkanes, prefix with alkyl substituents • side chain positions are based on the C in COOH being 1 e.g. CH3 - CH(CH3) - CH2 - CH2 - COOH is called 4-methylpentanoic acid

NAMING CARBOXYLIC ACIDS Acids are named according to standard IUPAC rules • select the longest chain of C atoms containing the COOH group; • remove the e and add oic acid after the basic name • number the chain starting from the end nearer the COOH group • as in alkanes, prefix with alkyl substituents • side chain positions are based on the C in COOH being 1 METHANOIC ACID ETHANOIC ACID PROPANOIC ACID

NAMING CARBOXYLIC ACIDS Acids are named according to standard IUPAC rules • select the longest chain of C atoms containing the COOH group; • remove the e and add oic acid after the basic name • number the chain starting from the end nearer the COOH group • as in alkanes, prefix with alkyl substituents • side chain positions are based on the C in COOH being 1 BUTANOIC ACID 2-METHYLPROPANOIC ACID

NAMING CARBOXYLIC ACIDS Acids are named according to standard IUPAC rules Many carboxylic acids are still known under their trivial names, some having been called after characteristic properties or their origin. Formula Systematic name (trivial name) origin of name HCOOH methanoic acid formic acid latin for ant CH3COOH ethanoic acid acetic acid latin for vinegar C6H5COOH benzenecarboxylic acid benzoic acid from benzene

Increases as size increases - due to increased van der Waals forces PHYSICAL PROPERTIES BOILING POINT Increases as size increases - due to increased van der Waals forces 101°C 118°C 141°C 164°C

PHYSICAL PROPERTIES BOILING POINT Increases as size increases - due to increased van der Waals forces 101°C 118°C 141°C 164°C Boiling point is higher for “straight” chain isomers. 164°C 154°C Greater branching = lower inter-molecular forces = lower boiling point

PHYSICAL PROPERTIES BOILING POINT Increases as size increases - due to increased van der Waals forces Carboxylic acids have high boiling points for their relative mass The effect of hydrogen bonding on the boiling point of compounds of similar mass Compound Formula Mr b. pt. (°C) Comments ethanoic acid CH3COOH 60 118 propan-1-ol C3H7OH 60 97 h-bonding propanal C2H5CHO 58 49 dipole-dipole butane C4H10 58 - 0.5 basic V der W

PHYSICAL PROPERTIES BOILING POINT Increases as size increases - due to increased van der Waals forces Carboxylic acids have high boiling points for their relative mass • arises from inter-molecular hydrogen bonding due to polar O—H bonds AN EXTREME CASE... DIMERISATION • extra inter-molecular attraction = more energy to separate molecules HYDROGEN BONDING

PHYSICAL PROPERTIES SOLUBILITY • carboxylic acids are soluble in organic solvents • they are also soluble in water due to hydrogen bonding HYDROGEN BONDING

PHYSICAL PROPERTIES SOLUBILITY • carboxylic acids are soluble in organic solvents • they are also soluble in water due to hydrogen bonding • small ones dissolve readily in cold water • as mass increases, the solubility decreases • benzoic acid is fairly insoluble in cold but soluble in hot water HYDROGEN BONDING

PREPARATION OF CARBOXYLIC ACIDS Oxidation of aldehydes RCHO + [O] ——> RCOOH Hydrolysis of esters RCOOR + H2O RCOOH + ROH Hydrolysis of acyl chlorides RCOCl + H2O ——> RCOOH + HCl Hydrolysis of nitriles RCN + 2 H2O ——> RCOOH + NH3 Hydrolysis of amides RCONH2 + H2O ——> RCOOH + NH3

CHEMICAL PROPERTIES ACIDITY weak acids RCOOH + H2O(l) RCOO¯(aq) + H3O+(aq) form salts RCOOH + NaOH(aq) ——> RCOO¯Na+(aq) + H2O(l)

CHEMICAL PROPERTIES ACIDITY weak acids RCOOH + H2O(l) RCOO¯(aq) + H3O+(aq) form salts RCOOH + NaOH(aq) ——> RCOO¯Na+(aq) + H2O(l) The acid can be liberated from its salt by treatment with a stronger acid. e.g. RCOO¯ Na+(aq) + HCl(aq) ——> RCOOH + NaCl(aq) Conversion of an acid to its water soluble salt followed by acidification of the salt to restore the acid is often used to separate acids from a mixture.

CHEMICAL PROPERTIES ACIDITY weak acids RCOOH + H2O(l) RCOO¯(aq) + H3O+(aq) form salts RCOOH + NaOH(aq) ——> RCOO¯Na+(aq) + H2O(l) The acid can be liberated from its salt by treatment with a stronger acid. e.g. RCOO¯ Na+(aq) + HCl(aq) ——> RCOOH + NaCl(aq) Conversion of an acid to its water soluble salt followed by acidification of the salt to restore the acid is often used to separate acids from a mixture. QUALITATIVE ANALYSIS Carboxylic acids are strong enough acids to liberate CO2 from carbonates Phenols are also acidic but not are not strong enough to liberate CO2

ESTERIFICATION Reagent(s) alcohol + strong acid catalyst (e.g. conc. H2SO4 ) Conditions reflux Product ester Equation e.g. CH3CH2OH(l) + CH3COOH(l) CH3COOC2H5(l) + H2O(l) ethanol ethanoic acid ethyl ethanoate

ESTERIFICATION Reagent(s) alcohol + strong acid catalyst (e.g. conc. H2SO4 ) Conditions reflux Product ester Equation e.g. CH3CH2OH(l) + CH3COOH(l) CH3COOC2H5(l) + H2O(l) ethanol ethanoic acid ethyl ethanoate Notes Conc. H2SO4 is a dehydrating agent - it removes water causing the equilibrium to move to the right and thus increases the yield of the ester

ESTERIFICATION Reagent(s) alcohol + strong acid catalyst (e.g conc. H2SO4 ) Conditions reflux Product ester Equation e.g. CH3CH2OH(l) + CH3COOH(l) CH3COOC2H5(l) + H2O(l) ethanol ethanoic acid ethyl ethanoate Notes Conc. H2SO4 is a dehydrating agent - it removes water causing the equilibrium to move to the right and thus increases the yield of the ester Naming esters Named from the original alcohol and carboxylic acid CH3OH + CH3COOH CH3COOCH3 + H2O from ethanoic acid CH3COOCH3 from methanol METHYL ETHANOATE

CHLORINATION OF CARBOXYLIC ACIDS Chlorination involves replacing the OH with a Cl Product acyl chloride Reagent thionyl chloride SOCl2 Conditions dry conditions Equation CH3COOH + SOCl2 ——> CH3COCl + SO2 + HCl

ESTERS Structure Substitute an organic group for the H in carboxylic acids Nomenclature first part from alcohol, second part from acid e.g. methyl ethanoate CH3COOCH3 METHYL ETHANOATE ETHYL METHANOATE

ESTERS Structure Substitute an organic group for the H in carboxylic acids Nomenclature first part from alcohol, second part from acid e.g. methyl ethanoate CH3COOCH3 Preparation From carboxylic acids or acyl chlorides Reactivity Unreactive compared with acids and acyl chlorides METHYL ETHANOATE ETHYL METHANOATE

ESTERS Structure Substitute an organic group for the H in carboxylic acids Nomenclature first part from alcohol, second part from acid e.g. methyl ethanoate CH3COOCH3 Preparation From carboxylic acids or acyl chlorides Reactivity Unreactive compared with acids and acyl chlorides Isomerism Esters are structural isomers of carboxylic acids METHYL ETHANOATE ETHYL METHANOATE

STRUCTURAL ISOMERISM – FUNCTIONAL GROUP Classification CARBOXYLIC ACID ESTER Functional Group R-COOH R-COOR Name PROPANOIC ACID METHYL ETHANOATE Physical properties O-H bond gives rise No hydrogen bonding to hydrogen bonding; insoluble in water get higher boiling point and solubility in water Chemical properties acidic fairly unreactive reacts with alcohols hydrolysed to acids

PREPARATION OF ESTERS - 1 Reagent(s) alcohol + carboxylic acid Conditions reflux with a strong acid catalyst (e.g. conc. H2SO4 ) Equation e.g. CH3CH2OH(l) + CH3COOH(l) CH3COOC2H5(l) + H2O(l) ethanol ethanoic acid ethyl ethanoate Notes Conc. H2SO4 is a dehydrating agent - it removes water causing the equilibrium to move to the right and thus increases the yield of the ester For more details see under ‘Reactions of carboxylic acids’

PREPARATION OF ESTERS - 2 Reagent(s) alcohol + acyl chloride Conditions reflux under dry conditons Equation e.g. CH3OH(l) + CH3COCl(l) ——> CH3COOCH3(l) + HCl(g) methanol ethanoyl methyl chloride ethanoate Notes Acyl chlorides are very reactive but must be kept dry as they react with water

PREPARATION OF ESTERS - 3 Reagent(s) alcohol + acid anhydride Conditions reflux under dry conditons Equation e.g. CH3OH(l) + (CH3CO)2O(l) ——> CH3COOCH3(l) + CH3COOH(l) methanol ethanoic methyl ethanoic anhydride ethanoate acid Notes Acid anhydrides are not as reactive as acyl chlorides so the the reaction is slower. The reaction is safer - it is less exothermic. Acid anhydrides are less toxic.

Hydrolysis is the opposite of esterification HYDROLYSIS OF ESTERS Hydrolysis is the opposite of esterification ESTER + WATER CARBOXYLIC ACID + ALCOHOL HCOOH + C2H5OH METHANOIC ETHANOL ACID ETHYL METHANOATE

Hydrolysis is the opposite of esterification HYDROLYSIS OF ESTERS Hydrolysis is the opposite of esterification ESTER + WATER CARBOXYLIC ACID + ALCOHOL HCOOH + C2H5OH METHANOIC ETHANOL ACID ETHYL METHANOATE METHYL ETHANOATE

Hydrolysis is the opposite of esterification HYDROLYSIS OF ESTERS Hydrolysis is the opposite of esterification ESTER + WATER CARBOXYLIC ACID + ALCOHOL HCOOH + C2H5OH METHANOIC ETHANOL ACID ETHYL METHANOATE CH3COOH + CH3OH ETHANOIC METHANOL ACID METHYL ETHANOATE

HYDROLYSIS OF ESTERS Hydrolysis is the opposite of esterification ESTER + WATER CARBOXYLIC ACID + ALCOHOL The products of hydrolysis depend on the conditions used... acidic CH3COOCH3 + H2O CH3COOH + CH3OH alkaline CH3COOCH3 + NaOH ——> CH3COO¯ Na+ + CH3OH

HYDROLYSIS OF ESTERS Hydrolysis is the opposite of esterification ESTER + WATER CARBOXYLIC ACID + ALCOHOL The products of hydrolysis depend on the conditions used... acidic CH3COOCH3 + H2O CH3COOH + CH3OH alkaline CH3COOCH3 + NaOH ——> CH3COO¯ Na+ + CH3OH If the hydrolysis takes place under alkaline conditions, the organic product is a water soluble ionic salt

HYDROLYSIS OF ESTERS Hydrolysis is the opposite of esterification ESTER + WATER CARBOXYLIC ACID + ALCOHOL The products of hydrolysis depend on the conditions used... acidic CH3COOCH3 + H2O CH3COOH + CH3OH alkaline CH3COOCH3 + NaOH ——> CH3COO¯ Na+ + CH3OH If the hydrolysis takes place under alkaline conditions, the organic product is a water soluble ionic salt The carboxylic acid can be made by treating the salt with HCl CH3COO¯ Na+ + HCl ——> CH3COOH + NaCl

NATURALLY OCCURING ESTERS - TRIGLYCERIDES • triglycerides are the most common component of edible fats and oils • they are esters of the alcohol glycerol (propane-1,2,3-triol) Saponification • alkaline hydrolysis of triglycerol esters produces soaps • a simple soap is the salt of a fatty acid • as most oils contain a mixture of triglycerols, soaps are not pure • the quality of a soap depends on the oils from which it is made CH2OH CHOH

USES OF ESTERS Despite being fairly chemically unreactive, esters are useful as ... • flavourings apple 2-methylbutanoate pear 3-methylbutylethanoate banana 1-methylbutylethanoate pineapple butylbutanoate rum 2-methylpropylpropanoate • solvents nail varnish remover - ethyl ethanoate • plasticisers

ACYL CHLORIDES Nomenclature Named from the corresponding carboxylic acid remove -ic add -yl chloride CH3COCl ethanoyl chloride C6H5COCl benzene carbonyl (benzoyl) chloride Chemical Properties • colourless liquids which fume in moist air • attacked at the positive carbon centre by nucleophiles • these include water, alcohols, ammonia and amines • undergo addition-elimination reactions

ACYL CHLORIDES Reagent Water Product(s) carboxylic acid + HCl (fume in moist air / strong acidic solution formed) Conditions room temperature Equation CH3COCl(l) + H2O(l) ——> CH3COOH(aq) + HCl(aq) Mechanism addition-elimination

ACYL CHLORIDES Reagent Alcohols Product(s) ester + hydrogen chloride Conditions reflux in dry (anhydrous) conditions Equation CH3COCl(l) + CH3OH(l) ——> CH3COOCH3(l) + HCl(g) Mechanism addition-elimination

ACYL CHLORIDES Reagent Ammonia Product(s) amide + hydrogen chloride Conditions Low temperature and excess ammonia; vigorous reaction. Equation CH3COCl(l) + NH3(aq) ——> CH3CONH2(s) + HCl(g) or CH3COCl(l) + 2NH3(aq) ——> CH3CONH2(s) + NH4Cl(s) Mechanism addition-elimination

ACYL CHLORIDES Reagent Amines Product(s) N-substituted amide + hydrogen chloride Conditions anhydrous Equation CH3COCl + C2H5NH2 ——> CH3CONHC2H5 + HCl or CH3COCl + 2C2H5NH2 ——> CH3CONHC2H5 + C2H5NH3Cl Mechanism addition-elimination - similar to that with ammonia.

What should you be able to do? REVISION CHECK What should you be able to do? Recall and explain the physical properties of carboxylic acids Recall the structures of carboxylic acids, esters and acyl chlorides Recall the acidic properties of carboxylic acids Recall and explain the esterification of carboxylic acids Write balanced equations representing any reactions in the section Recall and explain the structure and naming of esters Recall the methods for making esters Recall the conditions for, and products of, the hydrolysis of esters. CAN YOU DO ALL OF THESE? YES NO

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